1. Field of the Invention
The invention concerns a cosmetic composition which imparts a tan similar in color to a natural suntan onto the skin.
2. The Related Art
Today there is a great health concern with natural tanning through sunlight. Ultraviolet radiation from the sun is considered to be a leading factor in causing skin cancer. Even if not lethal, ultraviolet radiation has been acknowledged as accelerating aging and wrinkling processes on the skin.
Beyond health concerns, there are obvious practical reasons against natural tanning. Foremost is the reason that in many areas of the globe and during all but summertime, there is insufficient sunlight available to accomplish a natural tan.
Based on the above considerations, there has been much interest in effectuating a tan through cosmetic means. Dihydroxyacetone (hereinafter known as DHA) has widely been utilized in cosmetics to accomplish self-tanning of the skin. In the J. Soc. Cosmet. Chem., 35, pages 265-272 (August 1984), Bobin et al. studied the Maillard reaction of DHA with various amino acids found naturally in the hydrolipid film and first layers of the stratum corneum. The Maillard reaction method has commonly been utilized as an artificial tanning system since 1960.
Other studies on the Maillard reaction between DHA and amino acids have been reported in Agric. Biol. Chem., 44 (7), pages 1595-1599 (Kawashima et al.). Through this study it was determined that the rate of browning was maximum around a DHA-amino acid molar ratio of 1.5 when the total concentration of both reactants together was constant at 0.1M. Lysine and glycine were found to have the highest browning activity.
Another approach to the tanning problem is reported in Australian Patent 61950/90 to L'Oreal. The art had earlier appreciated that both DHA and 5,6-dihydroxy indole and certain of its derivatives would each independently cause coloration in the skin; the mechanisms were each believed to be different. The Australian patent teaches that a combination of these materials achieves a rapidly developed intense coloration much closer to the hue imparted by natural tanning than the colorations obtained with each of the compounds taken separately. Since DHA and indole are unstable in the presence of one another, the patent further suggested delivering these compounds from separate compartments of a multi-compartment kit.
Although there has been great progress in sunless self-tanning compositions as noted above, considerable further progress is needed to increase speed of coloration and achieve a coloration even closer to a natural tan. For medical safety reasons, it is also preferred to avoid use of indoles. Furthermore, many of the known self-tanning compositions have storage stability problems. DHA can rapidly decompose in many formulations. Streaking is a still further problem faced by the art. By the term "streaking" is meant noneven deposition on the skin; the tan coloration tends to migrate along an outer perimeter as a result of the formula being rubbed around upon the skin.
Accordingly, it is an object of the present invention to provide a composition and method for self-tanning having improved rates of coloration and imparting a more natural hue.
A further object of the present invention is to provide a composition and method for self-tanning which utilizes ingredients that impart good aesthetics and have an impeccable health safety profile.
A still further object of the present invention is to provide a composition and method for self-tanning which utilizes mutually compatible ingredients that do not decompose upon storage.
Still another object of the present invention is to provide a composition and method for self-tanning which avoids the streaking phenomena.
These and other objects of the present invention will become more readily apparent through the following summary, detailed discussion and Examples which follow.